The invention relates to a direct reading temperature measuring bridge circuit containing a platinum resistance type sensor for the highly precise measurement of temperature variations, particularly of very small temperature variations.
In the case of temperature measuring bridges diverse circuit arrangements have been proposed which are usually based on the principle of the Wheatstone bridge. The temperature sensor, i.e. transducer, used for accurate measurements is a platinum resistance type sensor which has a non-linear temperature-resistance characteristic approximately represented by the relationship R(x) = R.sub.1 (1+ .alpha.X+ .beta.X.sup.2), where R(x) is the resistance of the sensor at X.degree. C., R.sub.1 is the resistance at 0.degree. C., and .alpha. and .beta. are constants. The non-linearity of the sensor is an unfavorable property which must be compensated for in the measuring device. The measuring device must further be capable of being calibrated simply in such a way that when it is in a state of balance the increment of a predetermined balancing resistor corresponds to the actual temperature change in the environment of the sensor.